Transverse constriction of the maxillary dental arch is a condition which results in nonalignment of the posterior upper and lower teeth. One common method of expanding the maxilla to produce proper biting alignment of the affected teeth involves controlled separation of the midpalatal suture by means of an expandable, force transmitting appliance which is attached to selected sets of opposing maxillary teeth. Gradual expansion of the appliance transmits laterally outward forces on the maxilla through the teeth which, over an extended period of time, eventually separates the midpalatal suture allowing movement of the maxilla to bring the teeth into the desired alignment. In children, the midpalatal suture is essentially open and becomes fused through natural physical development after puberty, consequently, a maxillary expansion appliance is often used in connection with children to separate the suture and expand the maxilla. This orthodontic technique is employed somewhat less frequently in the case of adults having constricted palates, since the midpalatal suture fuses at approximately 18 years of age and makes separation thereof impossible without oral surgical intervention for reopening the fused suture. After the suture is opened by surgical means, however, a maxillary expansion appliance may be installed in the adult patient's palate to separate the maxilla and bring the maxillary teeth into proper biting alignment. Palatal expansion appliances are also utilized in connection with the treatment of persons having improperly developed lateral palatal shelves which result in a condition known as cleft palate. The severe maxillary constriction caused by the cleft palate condition is frequently corrected through the use of the expansion appliance in combination with surgical and prosthetic reconstruction.
The complete impact and significance of the present invention becomes evident only upon a thorough understanding and appreciation of the prior orthodontic procedure by which a maxillary expansion appliance was fitted and installed between a patient's maxillae, which will now be discussed. It is first important to recall that the object of the appliance is to move the maxillae apart themselves, rather than moving the posterior teeth with respect to the bone structure thereunder forming the maxillae. With this in mind, it is desirable to avoid any movement of the affected maxillary teeth with respect to each other during the spreading of the midpalatal suture, and in fact, the orthodontist attempts to immobilize the mentioned teeth with respect to each other so that the lateral forces generated by the appliance are fully communicated to the maxillae rather than to the teeth themselves. These functional requirements, in addition to the limited range of known orthodontic techniques for fastening appliances to the teeth, have in the past dictated the need to use traditional orthodontic bands and brackets for immobilizing the affected teeth and for attaching the appliance thereto.
Patients with constricted palates, frequently children, often have close dental crowding of the maxillary teeth which makes it virtually impossible to fit the required orthodontic bands around such teeth. Consequently, the first step in the previous technique for fitting the appliance to the patient's teeth involved the procedure of wedging the teeth apart to produce interproximal spacing between the teeth which allowed the bands to be fitted and attached therearound. Several methods may be employed to wedge the teeth apart to accomplish the necessary spacing, but all of such procedures require an extended period of time to accomplish and are extremely uncomfortable for the patient. After separating the teeth interproximally, bands were then positioned around each tooth involved. With children, it is sometimes impossible to install a band around a particular tooth due to the fact that some teeth may not protrude sufficiently beyond a gum line to present an adequate surface area to which the band may be attached. Similarly, conical or malformed teeth are difficult, and in some cases impossible to band; consequently, under these circumstances, the maxillary expansion appliance could not be employed. In other cases, the teeth may extend only a marginal distance beyond the gum line in which case the bands were installed around the exposed tooth surface areas and were then forced downwardly along the tooth into the surrounding gum; this procedure, of course, was particularly uncomfortable for the patient. In any event, after having installed the bands around the affected teeth, an impression was taken of the teeth with the bands in place, after which the impression was removed from the patient's mouth. The bands were then removed from the patient's teeth and inserted into the impression, whereupon a dental gypsum material was poured into the impression to form a model of the patient's teeth with the bands properly fastened in position therearound. With the bands fastened around the model of the teeth, a wire frame structure was then soldered to the bands in order to form a rigid assembly structurally interconnecting each of the latter, and the assembly was then attached to an expansion screw mechanism to complete the appliance. The procedure of fastening the wire structure to the bands became rather critical in order to assure that the laterally outward force produced by the expansion appliance was evenly applied to each of the teeth in a uniform manner, rather than imposing differing magnitudes of force on the teeth which might result in orthodontic movement of the latter, rather than orthopedic movement of the maxilla. After interconnecting the bands by means of the wire structure, the affected teeth were again separated interproximally by means of wedging devices or the like before the appliance and attached band assembly could be fitted onto the patient's teeth. After having separated the teeth, an adhesive dental cement was then applied to the interior surfaces of the bands. The appliance and associated band assembly was then installed as a single unit and the bands were secured, by means of the dental cement, to the teeth.
From the foregoing, it can be readily appreciated that the use of traditional, orthodontic bands for installing the expansion appliance between the patient's maxillary teeth was not only very time-consuming (and therefore costly to the patient) and painful, but was also rather imprecise and subject to human error. In fact, the prior procedure for attaching the expansion appliance to the teeth was considerably less than completely satisfactory, since the individual bands would often break loose from their associated tooth during the course of the suture opening procedure; this was primarily due to the fact that the bands could not be installed as a unit around the teeth as tightly as they might be installed on an individual basis around the teeth. Moreover, since the bands had to be installed as a single unit, the bands had to be slightly oversized to provide a fitting tolerance to assure that all the bands could be installed around their associated teeth. The prior procedure is also undesirable from the standpoint that washing out of cement around the banded teeth predisposes the latter to decalcification and later possible tooth decay. Also, it was not uncommon for one or more of the bands to become loosened from its associated tooth; under these circumstances, the entire expansion appliance and associated band assembly had to be removed from the patient's mouth, while the teeth were cleaned and again prepared for refitting of the appliance as described above.